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Plesiosauria is a clade of medium to large bodied marine reptiles with a cosmopolitan distribution ranging from the latest Triassic to the end of the Cretaceous. In Europe, the fossil record of Plesiosauria is mainly known from the Northern latitudes, whereas it is much rarer from the Southern and Mediterranean areas. Here, we report the first articulated skeleton of an Italian plesiosaurian, from the Callovian–Oxfordian deposits of the Rosso Ammonitico Veronese Formation of Kaberlaba (Veneto). The specimen is referred to Pliosauridae based on the large size of the skull, compared to the appendicular skeleton, the presence of the lacrimal, and a distinct anterolateral projection of the prefrontal into the orbital margin. Mandibular and vertebral symplesiomorphies support the placement of the Italian taxon among the “gracile-longirostrine grade” of basal pliosaurids. The Kaberlaba plesiosaurian represents the second reptile clade recovered from the Rosso Ammonitico Veronese Formation, after Thalattosuchia.
A partial plesiosauroid skull from the São Gião Formation (Toarcian, Lower Jurassic) of Alhadas, Portugal is re−evaluated and described as a new taxon, Lusonectes sauvagei gen. et sp. nov. It has a single autapomorphy, a broad triangular parasphenoid cultriform process that is as long as the posterior interpterygoid vacuities, and also a unique character combination, including a jugal that contacts the orbital margin, a distinct parasphenoid–basisphenoid suture exposed between the posterior interpterygoid vacuities, lack of an anterior interpterygoid vacuity, and striations on the ventral surface of the pterygoids. Phylogenetic analysis of Jurassic plesiosauroids places Lusonectes as outgroup to “microcleidid elasmosaurs”, equivalent to the clade Plesiosauridae. Lusonectes sauvagei is the only diagnostic plesiosaur from Portugal, and the westernmost occurrence of any plesiosaurian in Europe.
Complete plesiosaur skeletons are relatively abundant in the Lower Jurassic of England and Germany, but are exceptional in France. A new specimen from Normandy (northern France), including incomplete skull, palate and mandible with several associated vertebrae, is here described and its pliosauroid affinities are discussed. Comparison of this new specimen with other plesiosaurians indicates that it belongs to a new genus and species: Cryonectes neustriacus. This new plesiosaurian taxon represents one of the most complete pliosaurids reported from the Pliensbachian, a stage that has yielded very few diagnostic plesiosaurian remains. Our preliminary phylogenetic analysis places Cryonectes in a basal position among Pliosauridae, and suggests that the radiation of this clade occurred several millions of years earlier than previously thought. This new taxon contributes to our understanding of Early Jurassic plesiosaur diversity.
Rhomaleosaurid plesiosaurians were a common and ecologically significant component of Early Jurassic marine faunas, primarily as large-bodied predators. They declined in abundance and made their last fossil appearance in the Middle Jurassic. However, the geographic pattern of rhomaleosaurid extinction has thus far been obscured by spatial bias in the Middle Jurassic marine reptile fossil record, which is strongly focussed on low-latitude European assemblages. We report two rhomaleosaurid specimens from the Callovian (late Middle Jurassic) of the UK and Russia. Along with Borealonectes from Arctic Canada, these are the youngest-known occurrences of rhomaleosaurids. The UK specimen is the first identified from the Callovian of Europe, despite intensive fossil sampling over almost 200 years and the recovery of hundreds of other plesiosaurian specimens. Its discovery indicates that rhomaleosaurids were present, but extremely rare, at low palaeolatitudes of the Callovian. The Russian specimen is one of relatively few marine reptile specimens from its mid-palaeolatitude assemblage, as is also true of Borealonectes, which occurs in a high-palaeolatitude marine assemblage. Furthermore, we suggest that a mid latitude southern hemisphere occurrence from the Callovian of Argentina, previously referred to Pliosauridae, in fact represents a rhomaleosaurid. These findings suggest that rhomaleosaurids were actually common elements of mid-high palaeolatitude marine faunas, indicating a geographically staggered pattern of declining rhomaleosaurid abundance, and demonstrating the apparent persistence of an archaic marine reptile group in cool, mid-high latitude environments of the Middle Jurassic. It is therefore possible that sustained Middle-Late Jurassic global warming accelerated the ultimate extinction of rho-maleosaurids. Our findings suggest that widening the geographical breadth of fossil exploration could considerably enhance current knowledge of Jurassic marine reptile evolution.
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